Aerial surveying of terrain has greatly simplified cartography in that the exact position of terrain features may be established through the utilization of the photographs which result from the aerial photography. In the past, predetermined objects on the ground have been premarked, usually through the utilization of paint such that these objects may be accurately located. However, the ready visibility of painted marks may be obscured either by their small size or by terrain features, with the marks not being readily apparent from visual inspection of the resulting photograph.
As illustrated in U.S. Pat. No. 3,162,103, incorporated herein by reference, the position of an object may be ascertained by providing a constant light source at the object whose position is unknown and by providing constant light sources at or adjacent objects at two other known positions. An aerial photograph of the scene depicts the positions of all three objects from which the position of the object of undetermined position may be readily ascertained relative to the position of the other two objects. In this patent, there is no apparatus for providing a single flash of light. Moreover, there is no synchronization between light source actuation and the timing for the aerial camera utilized.
As illustrated in U.S. Pat. Nos. 2,764,072 and 3,218,947, incorporated herein by reference, radio-controlled flash bombs have been utilized with an aerial camera for determining the position of the drop. It will be appreciated that in the systems described in these patents, the flash bomb is detonated well above the ground. Thus, in these patents, there is no prepositioning of the flash producing device relative to the terrain. Prepositioning of markers is important in cartography so that the exact location of the marker, vis-a-vis the rest of the terrain, may be ascertained.
Remotely-controlled flashbulbs or flashlamps have routinely been used to illuminate the scene being photographed. U.S. patents, incorporated herein by reference, relating to remote flashbulb or flashlamp actuation include U.S. Pat. Nos. 3,254,580; 3,295,426; and 3,307,107. It will be appreciated that the flashbulbs or flashlamps in these patents are used to provide background light and the bulbs are not themselves photographed.
The identification of known points on the ground is critical to all types of surveying, giving rise to the desirability of a simple, inexpensive marking system in which a highly visible indication is provided for the photograph taken of the terrain. Prepositioning is required so that appropriate positions on the ground may be accurately located with a view to, for instance, laying out streets, pipelines, electrical transmission lines, or, in the case of agriculture, the proper positioning of rows or furrows which define a field under cultivation. Moreover, location of personnel at sea or on the ground by a simple one-time identification method permits photographic interrogation of personnel location without giving away personnel position.